EP1459427A2

EP1459427A2 - Electric motor and method for the production thereof

Info

Publication number: EP1459427A2
Application number: EP02787864A
Authority: EP
Inventors: Günter KESTING; Andreas Möckel; Dieter Oesingmann; Ronald Schuder; Wilfried Wintzer
Original assignee: BSH Bosch und Siemens Hausgeraete GmbH
Current assignee: BSH Hausgeraete GmbH
Priority date: 2001-12-21
Filing date: 2002-11-28
Publication date: 2004-09-22
Also published as: US20050023917A1; DE10163544A1; WO2003055035A2; WO2003055035A3

Abstract

The invention relates to an electric motor and to a method for the production thereof. According to the invention, an electricmotor with improved electrical, magnetic and mechanical properties and especially mass-power ratio can be provided in addition to an economical method for the production thereof. The electricmotor is embodied as a permanent-magnet excited electricmotor (1) comprising a symmetrically built support (4) with pole gap excitations, wherein low height hM high energy magnets (3) are provided for excitation purposes.

Description

Electric motor and method for its production

The present invention relates to an electric motor and method for its production.

Commutator motors with electrical excitation and permanent magnet excitation are predominantly manufactured in the power range from a few watts to 3,000 W. The speed range of these motors is between 2,000 min ^"1 to 60,000 min ^{" 1} . Areas of application are, for example, low-voltage applications as power take-offs in vehicles and in battery-operated devices, as well as the large range of mains-connected household appliances, such as vacuum cleaners, washing machines, coffee grinders, kitchen machines, etc., and hand tools such as drilling and grinding machines.

A commutator motor consists of a stator, which carries the excitation system, and a rotor, which is manufactured as an external or internal rotor. The permanent magnet excited motors largely occupy the speed range up to 10,000 min ^"1 and in some cases up to 20,000 ^{" 1} min, while the electrically excited motors have their main area of application in the upper speed range.

Compared to the electrically excited motors, the permanent magnet excited motors are characterized by a significantly simplified structure and associated with lower manufacturing costs. In addition, there are always losses in the stator windings of electrically excited motors which, due to the principle, cannot occur with permanent magnet excited motors, so that permanent magnet excited motors have an improved efficiency.

Most permanent magnet excited motors are currently manufactured with anisotropic ceramic magnets. The motor cross section is primarily circular. It only deviates from a circular shape in some two-pole motors due to flattening in the pole gaps. The often used term "flat motor" refers to this design. The diameter and length of such permanent magnet excited motors largely depend on the application, with only one of the design of the magnetic circuit can both be specified. The rotor design is characterized by the number of slots and commutators, which are chosen to be as small as possible to limit manufacturing costs.

The design of the motors is primarily based on the magnetic relationships and the material-economic data derived from them. With the optimization efforts it should be noted that some dimensions are not optimization parameters. These include:

• minimum air gap length of δ «0.5 mm • smallest magnet height from approx. 1 mm to approx. 4.5 mm

• Use of pole segments with a pole arc of maximum α _P = 145 °

The design of the magnets as pole segments, which are positioned directly at the air gap, guarantees the lowest scattering factor. The component that can save the most weight is the stator yoke, which can represent the motor housing and assembly level at the same time. This results in yokes that are often too thin from a magnetic point of view, which are also desirable because the processing of thin sheets is associated with lower production costs. The disadvantage, the limitation of the air gap flow, is accepted.

The design of the stator yokes of permanent magnet excited motors is characterized in an extreme way by the efforts to be able to produce the motors as inexpensively as possible. This is reflected in the manufacturing technologies of the stand yokes, such as:

• Machining production

• Cutting-bending process

• Roll

• deep drawing.

For these processes, one-piece semi-finished products serve as the starting material, which are deformed and designed and remain in one piece as a stand yoke. Due to the nature of the Stator yokes take over the functions of motor housings at the same time. These solutions are made possible not only because only constant fluxes and no eddy currents occur in the stator, so that no losses occur even in solid iron, but because the rotor diameters are so small that the fluxes of the magnets used so far have yoke strengths of up to b _S = 3 mm are sufficient. These material thicknesses can be controlled with the metal processing methods mentioned above.

The stand yokes are made of solid material for test samples or small series. The machining or machining processes used for this purpose are usually replaced in series production by more cost-effective non-cutting shapes.

Cutting-bending processes are used for stand yokes that are required when using block magnets. They consist of two equal parts, each with one or two flat sections and a curved area.

Rolled yokes are used for both circular and flattened contours of the stands. They can be of any length in the axial direction and up to yoke thicknesses of 3 mm. Adjustments to different laminated core lengths are easily possible. Two bearing plates are necessary.

Drawn yokes, which form pot shapes, compete with rolled ones. They have considerable cost advantages with small rotor diameters, for which only small sheet thicknesses are required, and with short sheet packs, because the deformation effort is then not so great. With the pot shape, it is easier to maintain higher degrees of protection that relate to the penetration of dirt and water than with other constructions. However, a special tool set must be provided for each motor length. The costs for this increase significantly with the length of the pot, so that the expenses must be well calculated. The yokes, deviating from the round shape as a housing for flat motors, can also be formed using the deep-drawing process. The closed part of the pot serves to accommodate axial and radial bearings, so that a bearing plate is saved as a separate component. The electrically excited motors are structurally characterized by the fact that the ferromagnetic parts of the stator and rotor are laminated cores that have a low axial magnetic conductivity and are therefore of the same length. The winding heads take up a lot of space, whereby the magnetic properties of the stator yokes and the rotor laminated core are not considered further.

It is an object of the present invention to further develop an electric motor while improving its electrical, magnetic, structural and mechanical properties and in particular the mass-performance ratio and to create an economical process for its production, the field of application of the permanent magnet excited motors being expanded ,

This object is achieved according to the invention by an electric motor with the features of claim 1 and a method according to claim 10. Advantageous developments of the invention are the subject of the respective subclaims.

An electric motor according to the invention is therefore characterized in that it is a permanent magnet-excited electric motor which has a symmetrically constructed stator with pole gap excitation and in which low-energy high-energy magnets are provided for excitation. The invention is essentially based on the following findings:

Low yoke strengths of the stator, to which the dimensions of the rotor are also coordinated, are often the reason in state-of-the-art motors that the replacement of ceramic magnets with high-energy magnets without changing the basic design does not lead to significant increases in performance. Higher magnetic material costs for high-energy magnets are not adequately compensated for by lower mass-performance ratios. A symmetrical design with pole gap magnets slightly simplifies the manufacture of such motors and has the smallest geometrical dimension in the polar axis.

In one embodiment of the invention, side-earth magnets are provided as high-energy magnets, in particular neodymium-iron-boron magnets. The replacement of ceramic magnets with neodymium-iron-boron magnets advantageously leads not only to a reduction in the magnet volume, but also to an increase in the air gap flow. In order to is a magnetic volume of a high-energy magnet compared to ceramic magnets in a ratio of approximately 1:20.

The proposed forms of the high-energy magnets, rhombus or cuboid, are much easier to manufacture than pole half-shells. In addition, a high-energy magnet of a machine according to the invention is made very thin compared to a ceramic magnet and in particular has a magnet height of only approximately 1 mm to approximately 4.5 mm.

In a development of the invention, a high-energy magnet is arranged at an angle deviating from a normal to the air gap. The width of the motor can be reduced, in particular in the case of magnets that have approximately the length of the rotor radius, by not arranging them vertically but at an acute angle to the air gap. The magnets can be rotated in both pole gaps in the same way or in the opposite direction. This results in several options for adapting a respective outer shape of the motor for the structural integration of a motor according to the invention in one device.

The positioning of rare earth magnets on both sides to build up the air gap field in a two-pole machine according to the invention is thus, among other things, according to one or more of the above-mentioned features. with the following advantages:

• Compared to asymmetrical motors, the one-sided radial pull is canceled with improved conditions for storage and a reduction in noise; • Shortening the field lines and thus reducing the magnetic voltage drop in the stator yoke.

• Reduction of the dimensions in the polar axis or the axial length;

• Enlargement of the polar arc due to the small magnet thickness or height, which can be reduced to a thickness of up to approx. H _M «1mm. • Reduction of the pole-sensing torques because the cogging torques compared to the

State of the art can be reduced more effectively by means of smaller groove bevels; • Simple magnet shape compared to the pole segments of ceramic magnets

• Reduction of the brush bridge twist due to the smaller pole gap;

• Realization of stator yokes of any length with improvement of the flux concentration in the polar arch;

• Extension of the magnets in the radial and axial direction enables flux amplification and flux concentration;

• With these motors, the design of flat motors does not require the reduction of the polar arc as with current designs.

• The smallest external dimension is in the center of the pole.

If the axial dimensions of the stator and rotor are the same, then for the effective manufacture of such an electric motor while realizing one or more of the features mentioned above, a follow-up cutting tool can preferably be used, which punch-packs the stator and armature plate assembly to build up a symmetrical motor that is permanently magnetized by high-energy magnets performs.

Preferably, at least two parts of a stator with at least two or another even number of high-energy magnets are connected to one another by gluing and / or enveloping to form a one-piece stator.

An electric motor according to the invention thus enables the use of permanent magnet excited machines with high energy magnets in the entire speed and power range mentioned at the outset according to a uniform basic concept with a new large number of relatively freely adjustable geometric parameters.

Exemplary embodiments of the invention are explained in more detail below with the aid of the drawing, which shows the prior art. The drawing shows:

FIG. 1: a sketched representation of a known asymmetrical permanent-magnet excited electric motor with a five-groove armature; Figure 2 is a schematic view of the cross section of an electric motor according to the invention;

Figure 3: a typical cross section of a two-pole, permanent magnet excited motor;

Figure 4 shows a longitudinal section of the permanent magnet excited motor of Figure 3;

Figure 5 is a diagram showing the reduction of the air gap flow as a function of the overhang factor and

Figures 6a to 6d:

Sketches to illustrate possibilities for shaping the outer contour of a stand according to the invention with pole gap magnets with a dimensioned embodiment.

A series of developments in motors with pole gap excitation can be derived from the prior art, in which a horseshoe magnet was first replaced by an electrical excitation coil and finally with the development of anisotropic ceramic magnets by block magnets. In this sequence, the manufacturing costs, losses and sizes decreased steadily, whereby in the last stage of the development shown, the failure rates also decreased significantly due to the lack of wire breaks in the stand. Substantial manufacturing advantages resulted from replacing the cutting and bending parts with sheet metal packages, which can be punched and easy to assemble, whereby the replacement of ceramic magnets with high-energy magnets, for example on a neodymium-iron-boron basis, not only to reduce the magnet volume, but also leads to an increase in the air gap flow. Overall, however, a simple replacement of ceramic magnets by high-energy magnets in known electric motors without fundamental design changes does not lead to any noteworthy increases in performance, so that the higher magnetic material costs are not adequately compensated for by lower mass-performance ratios. The use of high-energy magnets is therefore restricted to relatively few fields of application. The illustration in FIG. 1 shows a sketched representation of a known asymmetrical permanently magnetically excited electric motor 1 with a five-groove engine Armature 2 as an example of a stator 4 of a motor 1 equipped with a high-energy magnet 3, which is used as a drive in a model train.

When designing almost all permanent magnet excited motors, the magnetic properties of the stator yokes and the rotor laminated core are discussed too little or not at all. A basic finding as a starting point for an electric motor according to the invention is, however, that the low yoke strengths of the stator, to which the dimensions of the rotor are also matched, often form the cause in motors according to the prior art that the replacement of ceramic magnets by high-energy magnets does not leads to significant increases in performance in such engines. For this reason, motors equipped with high-energy magnets are currently used primarily in applications in which a very small space is required, such as the motor according to FIG. 1 in a model railroad locomotive. The reduction in the space requirement of such motors is solely due to a significantly lower volume-flow ratio of the high-energy magnets compared to ceramic permanent magnets.

The technologically simple horseshoe shape of the stand 4 with distinguishable yoke and pole areas 5, 6 from FIG. 1 can be replaced by a symmetrical arrangement without increasing the magnet weight and the motor width B, as shown in the illustration in FIG. 2 in a sketched form. In motors of the type shown with pole gap magnets, the pole and yoke regions 5, 6 can hardly be separated, so that the magnetically active part of the stator 4 consists of the poles or pole elements and the magnets 3. The manufacturing processes of the stator poles are influenced by the application and the motor dimensions. The number of design options is relatively large and allows the use of different materials and manufacturing processes.

The typical cross section of a permanent magnet excited commutator motor is characterized by the grooved rotor, the magnet, which is located directly at the air gap as a shell magnet, and the yoke as an annular magnetic yoke, which also forms the housing, as shown in the illustration in Figure 3. This basic form can also be assumed for further considerations of exemplary embodiments of the invention. The longitudinal section of the motor of FIG. 3 is shown in FIG. 4. Measures for achieving the greatest possible utilization of the rotor volume are disclosed, the dimensions which limit the power being recognizable at the same time. The rotor lamination stack l _Fe has the smallest axial extent of the magnetically active parts. In order to make the flow through the rotor as large as possible, the permanent magnet is extended beyond the length of the laminated core, the ratio of the magnet length l _M and the laminated core length l _Fe in the range of from executed motors

^ - wl, 2 - / - l, 8 l ^l Fe. The magnetic inference made of solid steel, which constructively represents the housing, can guide the magnetic flux in three dimensions. For this reason, the necessary cross section can be represented by a large axial length l _S and small radial

Realize expansion b _JS . This favored simple and highly productive manufacturing processes, the limit of which was reached at b _JS = 3 mm thick yokes.

To reduce the flux density in the stator yoke, the axial length of the stator yoke is chosen to be greater than that of the permanent magnet. In the case of short motors in particular, this measure has a positive effect on the magnetic voltage drops in the stator. The simple and partly screwless mounting of the end shields on the stator yoke is a constructive aspect to extend the stator yokes beyond the winding heads and the brush holder. The magnetic flux is determined by the magnetic quality and the rotor surface. Due to the extension of the magnets beyond the rotor laminated core, the flow through the brush plane can only be increased to a limited extent because the path of the field lines through the air is becoming ever greater. Guide values for this can be found in the experimentally determined diagram in FIG. 5. The relative reduction in the air gap flow ΔΦ / Φ is shown as a function of the overhang factor l _Fe / l _M. A ratio of anchor diameter D _A to a respective anchor or iron length l _{FE is} specified as a parameter.

The stator yoke is extended on one side to beyond the commutator area, while on the other side the yoke extends beyond the package length only by the length of the winding head. The space in the axial extension of the magnets is unused on both sides, which is indicated in the illustration in FIG. 4 by the two brackets marked with U. The magnetic flux limited by the design of the motor due to several causes means that a small cross section of the rotor yoke is sufficient without reaching the saturation range. Therefore, there is a lot of winding space available in the slots of the rotor, which cannot be fully used due to thermal reasons or because of the limitation of the permissible counter fields due to the risk of demagnetization of the pole segments.

The motor diameter of two-pole motors is limited by the inexpensive stator yoke technologies currently used. An increase in performance is mainly achieved by extending the axial expansion of the entire motor. Increasing the magnetic flux through pole segments made of high-energy material without changing the basic construction is possible to a limited extent, but currently fails because of the costs. It must not be overlooked that the manufacturing costs of the pole segments increase disproportionately with their size and that the dimensional accuracy in the manufacture of such permanent magnetic ceramics is becoming increasingly problematic. Here, versions with pole gap magnets, in particular in embodiments according to FIG. 2, represent an alternative to the known motors with pole magnets.

In embodiments of the motors with pole gap magnets, the flux is also conducted from the overhang areas through ferromagnetic sections of the pole elements to the air gap. For this purpose, experimental and three-dimensional field calculations are used to determine optimal overhang factors and shapes of the pole elements. The axial length of the magnet can be chosen as long as the stator yoke. This enables optimal use of space with comparatively low overhang factors and very small external dimensions.

The pole gap magnets are located in a magnetic circuit in which there is an air gap of twice the air gap length 2 δ> 1 mm. When designing the motors and during production, installation tolerances and thickness tolerances of the magnets can be taken into account, which have only a minor effect on the operating point on the demagnetization characteristic. This makes it possible to manufacture high-energy magnets with regard to surface quality and magnet thickness, which, in contrast to ceramic magnets, do not require the surfaces to be ground. Because the largest areas of the magnets through the If the pole elements are covered and possibly sealed with an adhesive, the corrosion protection provided by the magnet manufacturer may also be less expensive.

A further direction of optimization for the motor dimensions is given by the fact that only demagnetizing counter-flows occur which are caused by the twisting of the brush bridges. Since these values are low, magnetic materials with high remanence but low coercive force can be used. Even large inrush currents do not demagnetize the magnets.

A major advantage of the pole gap magnet is that the air gap flow is not determined solely by the magnetic surface above the rotor, but a flux concentration is possible through axial or radial extension of the magnets.

The motor width can be reduced, in particular in the case of magnets which have approximately the length of the rotor radius, by not arranging them perpendicularly but also at an acute angle β to the air gap, see the illustration sequence in FIGS. 6a to 6c. The magnets can be rotated in both pole gaps in the same way or in the opposite direction, i.e. mirror or point symmetry. This opens up several options for constructively integrating the motor into a device. The overall result is a motor with the specific dimensions of the stator 4 according to the information in FIG. 6d. The outer dimension has been reduced from an electro-magnetically equivalent version according to FIG. 6a by 85 mm by inclining the magnets 3 by ß = 45 ° while the magnet dimensions remain the same by a dimension 2Δ to only 76 mm. The ßtänder 4 shown is in one embodiment composed of at least two ferromagic molded parts, which are connected with at least two high-energy magnets 3 to form an overall very compact stand with simple manufacture by gluing and / or enveloping with a housing.

The advantages of the selected design of an engine 1 according to the invention are illustrated once again by the sectional view in FIGS. 6a to 6d: a powerful and very compact engine results, the external dimensions of which relate to an overall design or other conditions and restrictions in an available space can be adapted within a device. The positioning of rare earth magnets on both sides to build up the air gap field in a symmetrical stator arrangement is associated with advantages, which are summarized below:

Due to the symmetry of the arrangement in the stator area, the one-sided radial pull on the armature is canceled out in relation to asymmetrical stands. This improves the conditions for storing the armature and reduces the noise level during operation. The arrangement of two magnets for pole gap excitation shortens the field lines, which leads to a reduction in the magnetic voltage drop.

The dimensions of an electric motor according to the invention can be reduced either in the pole gap axis or in the axial length. Due to the small magnet thickness of the high-energy magnets, the pole arc is enlarged so that it almost matches the entire pole pitch. Pole-sensing torques are reduced because the cogging torques can be reduced more effectively compared to the prior art by means of smaller slot bevels. The rhombic outer shape of high-energy magnets represents a much simpler magnet shape compared to the pole segments of ceramic magnets. A brush bridge twist made to improve commutation can be significantly reduced due to the smaller pole gap.

According to the invention, it is possible to realize stator yokes of any length while increasing the flux concentration in the polar arch.

Extending the magnets in the radial and / or axial direction enables flux amplification or flux concentration to be chosen almost freely. After all, the design of flat motors for these motors does not require the reduction of the polar arc, as is the case with current designs. LIST OF REFERENCE NUMBERS

1 engine

2 anchors

3 magnet

4 stands

5 yokes

6 pin

7 wave

8th

B Motor ready / outer diameter of the motor bω magnet width hwi magnet height

IM axial magnet length α _P polar arc ß angle of inclination of the magnet 3 with respect to the normal

Δ difference dimension δ air gap / air gap length

DA armature diameter / rotor diameter

D _w shaft diameter

IFΘ lamination length / iron length of anchor 2

IJS length of the Ständerjochs

U unused length

Claims

claims

1. Electric motor, characterized in that the electric motor is designed as a permanent magnet excited electric motor (1), which has a symmetrically constructed stand (4) with pole gap excitation, in which high-energy magnets (3) of low height (h _M ) are provided as magnets.

2. Electric motor according to claim 1, characterized in that a rare earth magnet is provided as high-energy magnet (3), in particular a neodymium-iron-boron magnet.

3. Electric motor according to one or both of the preceding claims, characterized in that a high-energy magnet (3) is designed as a rhombus or cuboid.

4. Electric motor according to one or more of the preceding claims, characterized in that a high-energy magnet (3) in a machine according to the invention is very thin compared to a ceramic magnet with a magnet height (h _M ) of approximately 1 mm to approximately 4.5 mm is trained.

5. Electric motor according to one or more of the preceding claims, characterized in that the axial stator yoke length (l _S ) substantially the axial length (l _M ) of the

Permanent magnet (3) corresponds.

6. Electric motor according to one or more of the preceding claims, characterized in that an overhang factor (l _Fe / lwι) with a relatively large ratio of magnet length

(l _M ) to a laminated core length (l _Fe ) of the rotor (2) are small in comparison to designs of motors with pole magnets.

7. Electric motor according to one or more of the preceding claims, characterized in that a high-energy magnet (3) at an angle (ß) deviating from a normal to the air gap (δ) is arranged.

8. Electric motor according to one or more of the preceding claims, characterized in that a laminated core length (l _Fe ) of the armature (2) is substantially equal to the axial

Length (l _M ) of the high-energy magnet (3) is selected and a quotient of these sizes is in particular in a range from approximately 0.5 to approximately 1.

9. Electric motor according to one or more of the preceding claims, characterized in that the electric motor (1) is designed as a two-pole machine.

10. A method for manufacturing an electric motor (1), which is built up of one or more of the preceding claims in particular for the realization of the features, characterized in that at substantially the same length (l _S) of the stator yoke (4) and Läuferblechpa- ket (l _Fe ) a sequential cutting tool is used, and a die cut package from

Stand (4) and armature (2) for the construction of a symmetrical motor (1) excited by high-energy magnets (3).

11. The method according to the preceding claim, characterized in that the stator (4) is composed of at least two ferromagnetic molded parts (4), which with at least two high-energy magnets (3) in particular to form a compact stator (4) with each other by gluing and / or envelopes can be connected to a housing.